Thursday, December 12, 2013

Will the fat-burning magic of 1g/day of yeast hydrolysate dissolve the fat that's still covering the last 2 packs?

It sounds like a marketing scam and I must warn you, one of the authors of a soon-to-be-published paper on the basis of which I came up with this headline is actually with a company that specializes in food additives.

This obviously warrants a heightened degree of suspicion, but it does not mean that the study results could or even must be doctored. I would thus suggest, we take a look at what the Korean scientists from Jeonju University, the University of Seoul, the Korea University and the Neo Cremar Company Ltd. actually did and found before we jump to any premature conclusions about the validity or non-validity of the data.

What exactly is yeast hydrolysate?

I guess, the first thing we have to address is what exactly it was Jung et al. administered to their 24 male and 30 female participants with body mass indices (BMI) of at least 25 kg/m² (the obesity cut off in the Asia-Pacific region is 25 kg/m²). To this end, it's best to look at how this "supplement" was produced (if you want the short version fast forward to the first red box ;-)

After incubation, the culture is centrifuged at 10,000g
for 20 minutes.

Immediately after the cells are removed from the centrifuge, they are suspended in 20 mM phosphate buffer (pH 7.0) and
hydrolyzed with 1000 units of bromelain at 30
C for 4 h.

The result of this third step actually is already a, but not yet the hydrolysate. To achieve the "good stuff", it is then centrifuged at 10,000g for 20 min. The small molecules which are then removed from the supernatant are then passed through a 10 kDa molecular-weight cutoff membrane and eventually lyophilized - et voilà!

"Hold on! So what do I need?" Before you hit the "too complicated button" at the bottom of this page, let me briefly point out that you don't need to understand or memorize the production process. The thing you have to look for, when you are shopping for corresponding products is a yeast hydrolysate with a maximal molecular weight (that's ~ the size of the indiv. peptides) of <10kDa that was produced from Saccharomyces cerevisiae.

In the study at hand, the of this 3+1 step process was packed into 500 mg pouches before it was handed over to the subjects in the active arm of the study (the placebo contained dextrin).

Both the placebo and yeast supplements had to be taken twice a day 30 min before breakfast and dinner. So far that all sounds like standard procedure. If you take a look at the outcome of the randomization process, you will yet see that there are non-negligible inter-group differences in body composition (see Figure 1): In conjunction with the high fat mass, the low body weight and lean mass of the ladies in the control group, could have significant effects on the change in body weight. Unfortunately, the scientists did not test the significance of this difference, but a 39% gap in lean body mass that comes hand in hand with a 13% higher fat mass can be expected to have a very relevant effect on the outcome of any dietary intervention.

Speaking of dietary interventions! there was no dietary intervention.

I know, it sounds hilarious, but there was no dietary intervention. All the participants had to do was to consume the 1g of yeast hydrolysate or the 1g of dextrin in 2x500mg servings 30 min before breakfast and dinner. That's at least what they were advised to do.

The data in Figure 2 does yet tell you that what they actually did (voluntarily, though) was "dieting". This is particularly true for the female study participants, who reached caloric deficits of 26% by week 6-8 and 28% by week 8-10. Against that background it's not that surprising that the statistical significant changes in body comp were only observed in the female study participants.

There are no effects on resting metabolic rate! The notion that the reduced energy intake is the main, if not the only driving force of the fat loss Jung et al. observed in the study at hand is supported by observations the researchers made in a previous study from 2011 (Jung. 2011a). In the said study, the 20 obese females (body fat >28%) in the yeast group did experience a non-significantly improved fat loss compared to the control group. They did yet also suffer from a "higher" reduction in resting metabolic race (-9.69kcal/day vs. -4.35kcal/day) - similarly non-significant as the weight loss difference, obviously.

This does not mean that the yeast extract doesn't work - quite the contrary, for the average individual who is neither willing nor able to adhere to a caloric deficit without the help of tools like this, it could actually come very handy. For the average physical culturist, it would yet obviously be more interesting if yeast hydrolysates had spot reducing qualities (learn more about spot reduction). And if we take another look at the full text of the study, we could actually argue that this is basically what the authors suggest, when they refer to the results of previous studies and state:

If you look at the study at hand, the question we would have to answer should thus read: Are the abdominal and total fat mass disproportionate. Or to say it differently: Did the subjects lose signifcantly more abdominal than total fat? And in view of the previously discussed problem: Did this vary between male and female participants? Unfortunately, the scientists didn't do us (or rather me) the favor of doing this for us, already. Therefore I had to do the calculations and plotting for Figure 3 myself:

As the text in the box in Figure 3 already tells you, the existing discrepancy between the reduction in total body fat and abdominal fat thickness does not necessarily "prove" the spot reducing prowess of yeast hydrolysate. We do after all know that in the chubbier folks the unhealthy fat in / on the midsection is usually the first to go.

Is the fat loss really localized?

Furthermore, a previous study by the same researchers clearly refutes the abdominal specific fat loss effects. The corresponding paper was published in 2011 in the Journal of Food and Biochemistry (Jung. 2011a; same paper I referenced in the box above), and despite the fact that the researchers observed a trend for an increase in weight loss within only 4 weeks on the same <10kDa yeast hydrolysate, the fat loss results of the obese women who participated in the study were at best triceps (-2.15 vs. -1.05mm reduction in skinfold thickness in yeast vs. control) and not belly specific (-1.70 vs. -1.08mm reduction in skinfold thickness in yeast vs. control).

Unfortunately, I cannot tell you whether the same can be said of the 2009 paper by Suh et al., because the online archive of the Journal of Food Science
and Nutrition, where it was published starts in March 2011. In view of the fact that it was not "ab-specific" in obese women, I really doubt that it will have has particularly pronounced effects on the waistline of female college students - a subject group of whom you would expect that they are at least somewhat closer to the fitness and leanness level of the average SuppVersity reader.

Is yeast hydrolysate an effective tool in your weight loss arsenal? A definitive answer to this question is yet still lacking. Personally, I would spend my money otherwise, because I have never had a problem with cutting back calories, when I decided that this is necessary to lose weight. If, on the other hand, you belong to those people who are constantly hungry, it may be worth trialling a once month supply of yeast hydrolysate caps (or sachets).

The only thing you should be prepared for is that it is not going to work if you don't diet. In all of the human studies I've seen so far, the weight loss went hand in hand with a reduction in calorie intake; and despite the fact that there is good evidence that the His-Pro (=Cyclo) peptides in yeast hydrolysates have additional value as potent antioxidants (Jung. 2011b), their subsequent effect on glucose metabolism will depend on a baseline increase in inflammation. In other words: The bigger your belly, gluttony and baseline inflammation, the greater the benefits.

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